Metacrangon spinidorsalis, Komai & Taylor, 2010

Komai, T. & Taylor, J., 2010, Three new species of the crangonid genus Metacrangon Zarenkov (Crustacea: Decapoda: Caridea) from Australia, Memoirs of Museum Victoria 67, pp. 45-59 : 52-58

Metacrangon spinidorsalis sp. nov.

Metacrangon sp. ( Poore, 2004, 139, fig. 36f)

Metacrangon sp. MoV 5423. ( Poore et al., 2008, 81)

Figures 6–10

Material examined. Holotype: Australia, Western Australia, off Point Hillier (35°22.54'S, 117°12.25'E – 35°22.54'S, 117°12.25'E), 539 m, 22 Nov 2005, FRV Southern Surveyor , beam trawl (stn SS10/2005/019), WAM C45115 (1 female, cl 10.4 mm).

Paratypes: Tasmania, Tasman Sea off Maria Island (42°42.8'S, 148°22.2'E), 450 m, 25 Jun 1984, RV Soela , demersal beam trawl (stn S03/84/77), NMV J40886 (1 female, cl 7.6 mm); Southern Ocean , 48 km west of Richardson Point (41°15.0'S, 144°08.0'E), 520 m, 20 Oct 1984, Frank and Bryce demersal trawl (stn S05/84/51), NMV J40954 (1 female, cl 9.0 mm) . Western Australia, off Point Hillier (35°22.54'S, 117°12.25'E – 35°22.54'S, 117°12.25'E), 539 m, 22 Nov 2005, FRV Southern Surveyor, beam trawl (stn SS10/2005/019), NMV J54497 (3 females, cl 5.4–10.4 mm, 6 males, cl 6.1–7.0 mm); off Bald Island (35°04.01'S, 118°39.50'E – 35°13.40'S, 118°40.30'E), 728– 710 m, 23 Nov 2005 (stn SS10/2005/032), NMV J19215 (1 female, cl 7.7 mm); (35°12.49'S, 118°39.04'E – 35°12.14'S, 118°40.08'E), 431– 408 m, 24 Nov 2005 (stn SS10/2005/034), WAM C45116 (1 female, cl 6.9 mm); off Perth Canyon (31°59.33'N, 115°10.59'E – 32°00.07'S, 115°10.41'E), 508– 478 m, 29 Nov 2005 (stn SS10/2005/068), NMV J54512 (4 females cl 6.7–9.5 mm, 1 male cl 6.5 mm) .

Description. Female. Body (fig. 6) moderately robust. Rostrum (figs 7a–b) narrowly triangular with acute apex in dorsal view, directed forward, 0.20–0.25 times as long as carapace; dorsal surface nearly flat; lateral margin slightly arched in lateral view, merging into postorbital region of carapace; midventral carina low, ventral margin slightly sinuous in lateral view. Carapace (figs 6, 7a) slightly widened posteriorly, slightly longer than wide postorbitally; surface covered with very short setae; dorsal midline with two moderately small teeth; anterior tooth arising at rostral base, not overlapping rostrum, slightly larger than posterior (cardiac) tooth; posterior (cardiac) tooth arising at 0.55–0.60 of carapace length; submedian teeth moderately small; hepatic tooth relatively small; antennal tooth moderately strong, directed forward in dorsal view, somewhat ascending in lateral view (angle about 30° against horizontal plane of carapace), acuminate, far falling short of rostral apex; orbital cleft present, but only weakly delimited; anterolateral margin between antennal and branchiostegal tooth concave, with tiny spinule inferior to base of antennal tooth; branchiostegal tooth moderately strong, directed forward in dorsal view and somewhat dorsally in lateral view, reaching dorsodistal margin of antennal basicerite; pterygostomial tooth small, not visible in lateral view; postorbital carina clearly delimited, accompanied by longitudinal suture; epibranchial carina weakly delimited.

In spawning molts, thoracic sternum concave, armature absent; only fifth sternite with small tubercles medially. In nonspawning molts, fifth sternite with sharp, procurved tooth; sixth to seventh somites each with rounded, strongly compressed prominence, becoming higher posteriorly.

Abdomen (figs 6, 7c) slightly sculptured; anterior two somites without trace of middorsal carina anteriorly, but second tergum with distinct spiniform middorsal tooth located at anterior end of posterior section; third somite with trace of middorsal carina, and fourth somite with broad, clearly delimited middorsal carina. First and second pleura each with blunt tooth on ventral margin; third pleuron with blunt tooth at anteroventral angle; fourth pleuron unarmed. Fifth somite with low, but distinct middorsal carina; posterodorsal margin faintly produced medially; posterolateral margin unarmed; pleuron with posteroventral angle subacutely pointed, ventral margin gently convex. Sixth somite with distinct, straight submedian carinae, not reaching posterodorsal margin; dorsolateral carina distinct, reaching to posterodorsal margin; posterodorsal margin produced, faintly bilobed; pleuron flared laterally, posteroventral tooth small, acute or subacute; posterolateral process strong, directed slightly laterally, terminating in sharp tooth. Telson (fig. 7c) longer than sixth somite, tapering to acute tip; dorsal surface deeply grooved mesially, with three pairs of lateral spines, anterior-most pair located at about midlength; two plumose setae posterior to third pair of lateral spines (fig. 7d).

In spawning molt, first to fourth abdominal sternites unarmed; fifth sternite with low median tubercle. Sixth abdominal sternite shallow depressed medially.

Eye (figs 7a–b) slightly longer than wide; cornea slightly wider than eyestalk, light brown or opaque in preservative, corneal width 0.14–0.15 of carapace length; eyestalk with small, papilla-like dorsal tubercle.

Antennular peduncle (figs 7a–b) moderately stout, overreaching midlength of antennal scale. First segment with prominent, blunt distolateral process directed dorsally; distomesial margin unarmed; stylocerite falling slightly short of distolateral process, acutely or subacutely pointed, lateral margin gently convex. Second segment slightly widened distally, distinctly longer than wide, with prominent, blunt distolateral process. Third segment wider than long. Outer flagellum overreaching distal margin of lamella of antennal scale by about 0.4 length, consisting of 10–11 articles.

Antennal basicerite (fig. 7e) stout, with sharply pointed dorsodistal lateral angle and short ventrolateral tooth slightly overreaching dorsodistal lateral angle; carpocerite subcylindrical, reaching distal 0.20 of antennal scale. Antennal scale (figs 7a, 7e) about 0.50 times as long as carapace and 2.3 times longer than wide; lateral margin faintly sinuous; distolateral tooth relatively wide, slightly falling short of rounded distal margin of lamella.

Third maxilliped (fig. 8a) relatively slender, overreaching antennal scale by 0.6 length of ultimate segment; margins and dorsal surface of distal two segments with numerous short to long setae. Ultimate segment gradually tapering distally, 6.5–7.0 times longer than wide. Penultimate segment about 2.6 times longer than wide. Antepenultimate segment sinuously curved in dorsal view, with thick tuft of long setae dorsodistally; ventral surface with two minute spiniform setae subdistally (fig. 8b). Coxa with rounded lateral process (not figured). Exopod falling far short of distal margin of antepenultimate segment, with welldeveloped flagellum.

First pereopod (figs 8c–d) moderately stout, reaching distal margin of antennal scale; palm 3.0–3.5 times longer than wide, not widened proximally or distally, cutting edge oblique; lateral and mesial margins nearly straight; thumb moderately broad; carpus with small ventrolateral tooth, otherwise unarmed on lateral margin; merus with small dorsodistal tooth, ventral margin sinuous, crested. Second pereopod (fig. 8e) reaching nearly to midlength of antennal scale; dactylus about 0.5 times as long as palm; cutting edges of fingers with row of minute spiniform setae (fig. 8f); length ratio of chela to ischium 1:1.9:1.6:1.5; coxa with prominent flap-like process (not figured). Third pereopod (fig. 8g) slender, nearly reaching distal margin of antennal scale by tip of dactylus; length ratio of dactylus to ischium 1:2.2:4.6:2.9:3.2. Fourth pereopod (fig. 8h) moderately stout, slightly overreaching midlength of antennal scale by dactylus; dactylus (fig. 8i) spatulate, about 0.8 times as long as propodus, upper margin with row of dense stiff setae, lower margin with few sparse setae; tip of dactylus terminating in two unequal projections flanking unguis, upper projection longer, with minute setae; dactylus– propodus articulation about 45°; propodus about 3.6 times longer than wide, bearing row of dense stiff setae on dorsal and ventral margins; carpus shorter than propodus, with numerous long setae on dorsal margin; row of long setae on dorsal and ventral margins of merus and ischium (dorsal setae longer than ventral setae). Fifth pereopod (fig. 8j) distinctly shorter than fourth pereopod, falling far short of base of branchiostegal tooth; dactylus (fig. 8k) subspatulate, shorter than dactylus of fourth pereopod, about 0.6 times as long as propodus; setation much less than in fourth pereopod.

Uropod (fig. 6) not reaching tip of telson; exopod with nearly straight lateral margin, posterolateral angle terminating in truncate tooth(fig.8l); no movable spinule mesial to posterolateral tooth; endopod longer and narrower than exopod.

Male. Rostrum nearly spiniform (fig. 9A), 0.25–0.35 times as long as carapace, slightly overreaching distal corneal margins. Carapace (figs 9a–b) with two prominent middorsal teeth, anterior tooth elongate, arising slightly anterior to or just at level of posterior margin of orbit, overlapping rostrum; posterior tooth strong, hooked; branchiostegal tooth strong, curved slightly laterally, distinctly overreaching distolateral angle of antennal basicerite. Fifth to eighth thoracic sternites (fig. 9c) with prominent, acute teeth becoming larger posteriorly.

Middorsal tooth on second abdominal somite larger than in female; pleural ventral teeth on anterior three somites more pronounced in females (fig. 9d).

Corneal width 0.18–0.20 of carapace length (fig. 9a). Outer antennular flagellum (fig. 9a–b) overreaching antennal scale by 0.8 length, consisting of 15–18 articles. Antennal scale (fig. 9a) 0.55–0.60 times as long as carapace; distolateral tooth distinctly overreaching distal lamella.

Fourth pereopod (fig. 9e) more slender than in females (propodi about 4.5 times longer than wide); dactylus (fig. 9f) narrowly spatulate.

Endopod of first pleopod (fig. 9g) tapering distally to rounded tip, bearing four stiff setae terminally. Second pleopod with appendix masculina reaching about distal 0.6 of endopod, bearing about 10 long spiniform setae (fig. 9h).

Colouration. Carapace, abdominal somites, pereopods, telson and uropods relatively uniform browny red colour. Body, legs and first pereopods covered with whitish pigment spots; similar spots also present, but less pronounced on generally paler second to fifth pereopods.

Distribution. The present material contains specimens from two rather distant localities, namely southwestern Australia and Tasmania, suggesting that this species is widely distributed in southern Australia, at depths of 408– 728 m.

Remarks. Asisapparentfromtheabovedescription, Metacrangon spinidorsalis sp. nov. shows considerable degree of sexual dimorphism in the development of the middorsal teeth on the carapace and the shape of the antennal scale.

This new species is referable to the Metacrangon jacqueti species group because of the disposition of teeth on the carapace, the presence of ventral tooth on each first to third abdominal pleuron, and the setose margins of the dactyli of the fourth and fifth pereopods ( Komai, 1997). The following nine species are referred to this informal species group ( Komai, 1997; Retamal and Gorny, 2003): M. agassizi ( Smith, 1882) from the northwestern Atlantic; M. bahamondei Retamal and Gorny, 2003 from southern part of Chile; M. bellmarleyi ( Stebbing, 1914) from western to southern Africa; M. crosnieri Komai, 1997 from Madagascar; M. jacqueti from the northeastern Atlantic; M. knoxi from the Chatham Rise, New Zealand; M. ochotensis ( Kobjakova, 1955) from the South Kuril Islands in the northwestern Pacific; M. procax ( Faxon, 1893) from California to Peru in the eastern Pacific; and M. similis Komai, 1997 from Japan. However, M. spinidorsalis is unique even within the genus, as it possesses a distinct middorsal tooth on the second abdominal tergite. Furthermore, in this new species, the orbital cleft is only weakly delimited. In this regard, this new species is intermediate between M. knoxi (where the orbital cleft is absent) and other species in the M. jacqueti species group (where the orbital cleft is distinct). The small anterior middorsal tooth on the carapace in females, which does not overlap the rostrum, also distinguishes M. spinidorsalis from other species in the M. jacqueti species group.

Etymology. Named in reference to the characteristic spiniform tooth on the second abdominal tergite.